The amorphous phase behavior of blends of poly(butylene terephthalate) (PBT) and polyester-ether) segmented block copolymers (PEE) was found to vary from completely immiscible to miscible, depending on the copolymer composition. The predictions of the Flory-Huggins relationship are in general agreement with the observed behavior when the interaction parameters are estimated from solubility parameters. The results of thermal analysis and small-angle X-ray scattering experiments strongly suggest that the PBT and PEE copolymers are capable of cocrystallization in the miscible blends under all crystallization conditions. The cocrystalline microstructure results from the complete miscibility and the blocky nature of the copolymer (i.e., the identical chemical and crystalline structures of the PEE hard segments and PBT). The crystallization rate of the copolymer in the miscible blends was found to be significantly enhanced due to the presence of PBT, and the resulting crystal thickness was found to be the same as that observed for PBT. Partially miscible blends of PBT with copolymers containing intermediate hard-segment concentrations formed distinguishable crystal populations, but the crystallization rate of the copolymer in these blends was also strongly influenced by the presence of PBT.
In this paper we focus on miscible blends of two engineering polymers: poly(butylene terephthalate) (PBT) and a polyarylate (PAr). The issue of transesterification in these blends will be addressed, followed by a discussion of the crystallization kinetics of PBT, poly(ethylene terephthalate) and several PBT/PAr blends. The ability to estimate polymer–polymer interaction parameters in blends from melting point depression will also be discussed. The amorphous phase behavior of the PBT/PAr blends has been explored primarily using dielectric spectroscopy. For blends in which PBT has crystallized, we observe two relaxations associated with Tg‐like motion, and this behavior is interpreted in light of our recent work on order–disorder interphases in crystalline blends.
Coupled thermal and carrier transport (electron/hole generation, recombination, diffusion and drifting) in laser photo-etching of GaAs thin film is investigated. A new volumetric heating mechanism originated from SRH (Shockley-Read-Hall) non-radiative recombination and photon recycling is proposed and modeled based on recent experimental findings. Both volumetric SRH heating and Joule heating are found to be important in the carrier transport as well as the etching process. SRH heating and Joule heating are primarily confined within the space charge region which is about 20 nm from the GaAs surface. Surface temperature rises rapidly as the laser intensity exceeds 105 (W/m2). Below a laser intensity of 105 (W/m2), thermal effect is negligible. The etch rate is found to depend on the competition between photo-voltaic and photo-thermal effects on surface potential. At high laser intensity, etch rate is increased by more than 100% due to the SRH and Joule heating.
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